Phase change random access memory (PCRAM) devices are widely used in electronic appliances as non-volatile memory devices due to their many advantages such as fast read/write access times, a large number of times of read/write operations, long data retention time, small unit area, and others. A PCRAM device typically includes resistance units and selector devices, which are used for selecting memory elements in the phase change memory. A selector device (referred to as selector hereinafter) can be a CMOS field effect transistor type, BJT type, or a PN junction diode type. Because a junction diode has a small cell size and provides a high programming voltage, a PCRAM device with diodes as selectors has a better performance than PCRAM devices with other types of selectors.
With ongoing development of semiconductor manufacturing technology, phase change memory devices are getting more densely integrated. As process nodes go below 40 nm, selectors will become the bottleneck in the manufacture of PCRAM devices. With the reduction in physical size, PN junction diodes have a higher turn-on voltage and sneak current. Thus, in order to use PN junction diodes in a PCRAM device, the problems of high turn-on voltage and sneak current must be solved.